Method and apparatus for sequence hopping in single carrier frequency division multiple access (SC-FDMA) communication systems

ABSTRACT

Methods and apparatuses are provided for transmitting and receiving a signal using a sequence in a wireless communication system. The method includes receiving, from a base station, information indicating whether sequence hopping is applied or not; transmitting, to the base station, the signal using a first sequence if a number of resource blocks allocated to the user equipment is less than a predetermined value; and transmitting, to the base station, the signal using a second sequence to which the sequence hopping is applied based on the received information if the number of the resource blocks allocated to the user equipment is greater than or equal to the predetermined value. The sequence hopping is performed using a pseudo-random function, and the sequence hopping is performed in a unit of a slot.

PRIORITY

This application is a Continuation Application of, and claims priorityunder 35 U.S.C. § 120 to, U.S. patent application Ser. No. 16/390,625,filed in the U.S. Patent and Trademark Office (USPTO) on Apr. 22, 2019,which is a Continuation Application of, and claims priority under 35U.S.C. § 120 to, U.S. patent application Ser. No. 15/399,396, filed inthe USPTO on Jan. 5, 2017, issued as U.S. Pat. No. 10,298,367 on May 21,2019, which is a Continuation Application of, and claims priority under35 U.S.C. § 120 to, U.S. patent application Ser. No. 14/827,646, filedin the USPTO on Aug. 17, 2015, issued as U.S. Pat. No. 9,572,164 on Feb.14, 2017, which is a Continuation Application of, and claims priorityunder 35 U.S.C. § 120 to, U.S. patent application Ser. No. 13/861,845,filed in the USPTO on Apr. 12, 2013, issued as U.S. Pat. No. 9,113,471on Aug. 18, 2015, which was a Continuation Application of, and claimspriority under 35 U.S.C. § 120 to, patent application Ser. No.12/203,432, filed in the USPTO on Sep. 3, 2008, issued as U.S. Pat. No.8,441,991 on May 14, 2013, which claims priority under 35 U.S.C. §119(e) to U.S. Prov. App. No. 60/969,659, filed in the USPTO on Sep. 3,2007, the entire content of each of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to wireless communicationsystems and, more particularly, to a Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) communication system that is furtherconsidered in the development of the 3^(rd) Generation PartnershipProject (3GPP) Evolved Universal Terrestrial Radio Access (E-UTRA) longterm evolution (LTE).

2. Description of the Art

Methods and apparatus are considered for the functionality andimplementation of hopping for sequences used in the construction ofReference Signals (RS) or control signals transmitted in SC-FDMAcommunication systems.

The Uplink (UL) of the communication system is assumed, whichcorresponds to signal transmissions from mobile User Equipments (UEs) toa serving base station (Node B). A UE, also commonly referred to asterminal or mobile station, may be fixed or mobile and may be a wirelessdevice, a cellular phone, a personal computer device, a wireless modemcard, etc. A Node B is generally a fixed station and may also be calleda Base Transceiver System (BTS), an access point, or some otherterminology. A Node B may control multiple cells in a cellularcommunication system, as it is known in the art.

Several types of signals need to be supported for the properfunctionality of the communication system. In addition to data signals,which convey the information content of the communication, controlsignals also need to be transmitted from UEs to their serving Node B inthe UL and from the serving Node B to UEs in the downlink (DL) of thecommunication system. The DL refers to the communication from the Node Bto UEs. Additionally, a UE having data or control transmission alsotransmits RSs, also known as pilots. These RSs primarily serve toprovide coherent demodulation for the transmitted data or controlsignals by a UE.

The UEs are assumed to transmit data or control signals over aTransmission Time Interval (TTI), which is assumed to correspond to asub-frame. The sub-frame is the time unit of a frame, which may consistof ten sub-frames. FIG. 1 illustrates a block diagram of the sub-framestructure 110. The sub-frame 110 includes two slots. Each slot 120further includes seven symbols used for transmission of data or controlsignals. Each symbol 130 further includes a Cyclic Prefix (CP) in orderto mitigate interference due to channel propagation effects. The signaltransmission in one slot may be in the same or at a different part ofthe operating bandwidth (BW) than the signal transmission in the secondslot. In addition to symbols carrying data or control information, somesymbols are used for Reference Signal (RS) transmission 140.

The transmission BW is assumed to include frequency resource units,which will be referred to herein as resource blocks (RBs). Each RB mayconsist of 12 sub-carriers and UEs are allocated a multiple N ofconsecutive RBs 150 for Physical Uplink Shared Channel (PUSCH)transmission and 1 RB for Physical Uplink Control Channel (PUCCH)transmission.

As the data or control signal transmission is over a BW that can be(orthogonally) shared by multiple UEs, the corresponding physical layerchannel may be respectively referred to as PUSCH or as PUCCH. FIG. 1illustrates a structure for the PUSCH sub-frame while respective onesfor the PUCCH will be subsequently described.

The UEs are also assumed to transmit control signals in the absence ofany data signals. The control signals include, but are not limited to,positive or negative acknowledgment signals (ACK or NAK, respectively)and Channel Quality Indication (CQI) signals. The ACK/NAK signals are inresponse to the correct or incorrect, respectively, data packetreception by a UE in the DL of the communication system. The CQI signalsare sent by a UE to inform its serving Node B of itsSignal-to-Interference and Noise Ratio (SINR) conditions in order forthe serving Node B to perform channel dependent scheduling in the DL ofthe communication system. Both ACK/NAK and CQI signals are accompaniedby RS signals in order to enable their coherent demodulation at the NodeB receiver. The physical layer channel conveying ACK/NAK or CQI controlsignaling may be referred as the PUCCH.

The ACK/NAK, CQI and associated RS signals are assumed to be transmittedby UEs in one RB using CAZAC sequences as it is known in the art and issubsequently described.

FIG. 2 shows a structure for the ACK/NAK transmission during one slot210 in a SC-FDMA communication system. The ACK/NAK information bits 220modulate 230 a “Constant Amplitude Zero Auto-Correlation (CAZAC)”sequence 240, for example with QPSK or 16QAM modulation, which is thentransmitted by the UE after performing an Inverse Fast Fourier Transform(IFFT) operation as it is further subsequently described. In addition tothe ACK/NAK, RS is transmitted to enable the coherent demodulation ofthe ACK/NAK signal at the Node B receiver. The third, fourth, and fifthSC-FDMA symbols in each slot may carry an RS 250.

FIG. 3 shows a structure for the CQI transmission during one slot 310 ina SC-FDMA communication system. Similar to the ACK/NAK transmission, theCQI information bits 320 modulate 330 a CAZAC sequence 340, for examplewith QPSK or 16QAM modulation, which is then transmitted by the UE afterperforming the IFFT operation as it is further subsequently described.In addition to the CQI, RS is transmitted to enable the coherentdemodulation at the Node B receiver of the CQI signal. In theembodiment, the second and sixth SC-FDMA symbols in each slot carry anRS 350.

As it was previously mentioned, the ACK/NAK, CQI, and RS signals areassumed to be constructed from CAZAC sequences. An example of suchsequences is the Zadoff-Chu (ZC) sequences whose elements are given byEquation (1) below:

$\begin{matrix}{{c_{k}(n)} = {{\exp\left\lbrack {\frac{j\; 2\;\pi\; k}{L}\left( {n + {n\frac{n + 1}{2}}} \right)} \right\rbrack}.}} & (1)\end{matrix}$

L is the length of the CAZAC sequence, n is the index of an element ofthe sequence n={0, 1, 2 . . . , L−1}, and k is the index of the sequenceitself. For a given length L, there are L−1 distinct sequences, if L isprime. Therefore, the entire family of sequences is defined as k rangesin {1, 2 . . . , L−1}. However, it should be noted that the CAZACsequences used for the ACK/NAK, CQI, and RS transmission need not begenerated using the exact above expression as it is further discussedbelow.

For CAZAC sequences of prime length L, the number of sequences is L−1.As the RBs are assumed to consist of an even number of sub-carriers,with 1 RB consisting of 12 sub-carriers, the sequences used to transmitthe ACK/NAK, CQI, and RS can be generated, in the frequency or timedomain, by either truncating a longer prime length (such as length 13)CAZAC sequence or by extending a shorter prime length (such as length11) CAZAC sequence by repeating its first element(s) at the end (cyclicextension), although the resulting sequences do not fulfill thedefinition of a CAZAC sequence. Alternatively, the CAZAC sequences canbe directly generated through a computer search for sequences satisfyingthe CAZAC properties.

A block diagram for the transmission through SC-FDMA signaling of aCAZAC-based sequence in the time domain is shown in FIG. 4. The selectedCAZAC-based sequence 410 is generated through one of the previouslydescribed methods (modulated by the respective bits in case of ACK/NAKor CQI transmission), it is then cyclically shifted 420 as it issubsequently described, the Discrete Fourier Transform (DFT) of theresulting sequence is obtained 430, the sub-carriers 440 correspondingto the assigned transmission bandwidth are selected 450, the InverseFast Fourier Transform (IFFT) is performed 460, and finally the CP 470and filtering 480 are applied to the transmitted signal 490. Zeropadding is assumed to be performed by a UE in sub-carriers used forsignal transmission by another UE and in guard sub-carriers (not shown).Moreover, for brevity, additional transmitter circuitry such asdigital-to-analog converter, analog filters, amplifiers, and transmitterantennas, as they are known in the art, are not shown in FIG. 4.Similarly, for the PUCCH, the modulation of a CAZAC sequence withACK/NAK or CQI bits is well known in the art, such as for example QPSKmodulation, and is omitted for brevity.

At the receiver, the inverse (complementary) transmitter functions areperformed. This is conceptually illustrated in FIG. 5 where the reverseoperations of those in FIG. 4 apply. As it is known in the art (notshown for brevity), an antenna receives the RF analog signal and afterfurther processing units (such as filters, amplifiers, frequencydown-converters, and analog-to-digital converters) the digital receivedsignal 510 passes through a time windowing unit 520 and the CP isremoved 530. Subsequently, the receiver unit applies an FFT 540, selects550 the sub-carriers 560 used by the transmitter, applies an Inverse DFT(IDFT) 570, de-multiplexes (in time) the RS and CQI signal 580, andafter obtaining a channel estimate based on the RS (not shown) itextracts the CQI bits 590. As for the transmitter, well known receiverfunctionalities such as channel estimation, demodulation, and decodingare not shown for brevity.

An alternative generation method for the transmitted CAZAC sequence isin the frequency domain. This is depicted in FIG. 6. The generation ofthe transmitted CAZAC sequence in the frequency domain follows the samesteps as the one in the time domain with two exceptions. The frequencydomain version of the CAZAC sequence is used 610 (that is the DFT of theCAZAC sequence is pre-computed and not included in the transmissionchain) and the cyclic shift 650 is applied after the IFFT 640. Theselection 620 of the sub-carriers 630 corresponding to the assignedtransmission BW, and the application of CP 660 and filtering 670 to thetransmitted signal 680, as well as other conventional functionalities(not shown), are as previously described for FIG. 4.

The reverse functions are again performed for the reception of theCAZAC-based sequence transmitted as in FIG. 6. This is illustrated inFIG. 7. The received signal 710 passes through a time windowing unit 720and the CP is removed 730. Subsequently, the cyclic shift is restored740, an FFT 750 is applied, and the transmitted sub-carriers 760 areselected 765. FIG. 7 also shows the subsequent correlation 770 with thereplica 780 of the CAZAC-based sequence. Finally, the output 790 isobtained which can then be passed to a channel estimation unit, such asa time-frequency interpolator, in case of a RS, or can be used fordetecting the transmitted information, in case the CAZAC-based sequenceis modulated by ACK/NAK or CQI information bits.

The transmitted CAZAC-based sequence in FIG. 4 or FIG. 6 may not bemodulated by any information (data or control) and can then serve as theRS, as shown, for example, in FIG. 2 and FIG. 3.

Different cyclic shifts of the same CAZAC sequence provide orthogonalCAZAC sequences. Therefore, different cyclic shifts of the same CAZACsequence can be allocated to different UEs in the same RB for their RSor ACK/NAK, or CQI transmission and achieve orthogonal UE multiplexing.This principle is illustrated in FIG. 8.

Referring to FIG. 8, in order for the multiple CAZAC sequences 810, 830,850, 870 generated correspondingly from multiple cyclic shifts 820, 840,860, 880 of the same root CAZAC sequence to be orthogonal, the cyclicshift value Δ 890 should exceed the channel propagation delay spread D(including a time uncertainty error and filter spillover effects). If Tsis the duration of one symbol, the number of cyclic shifts is equal tothe mathematical floor of the ratio Ts/D. For a CAZAC sequence of length12, the number of possible cyclic shifts is 12 and for symbol durationof about 66 microseconds (14 symbols in a 1 millisecond sub-frame), thetime separation of consecutive cyclic shifts is about 5.5 microseconds.Alternatively, to provide better protection against multipathpropagation, only every other (6 of the 12) cyclic shift may be usedproviding time separation of about 11 microseconds.

CAZAC-based sequences of the same length typically have goodcross-correlation properties (low cross-correlation values), which isimportant in order to minimize the impact of mutual interference insynchronous communication system and improve their receptionperformance. It is well known that ZC sequences of length L have optimalcross-correlation of √{square root over (L)}. However, this propertydoes not hold when truncation or extension is applied to ZC sequences orwhen CAZAC-based sequences are generated through computer search.Moreover, CAZAC-based sequences of different lengths have a widedistribution of cross-correlation values and large values can frequentlyoccur leading to increased interference.

FIG. 9 illustrates the Cumulative Density Function (CDF) ofcross-correlation values for length-12 CAZAC-based sequence resultingfrom cyclically extending a length-11 ZC sequence, truncating alength-13 ZC sequence and generating length-12 CAZAC-based sequencesthrough a computer search method. Variations in cross-correlation valuescan be easily observed. These variations have even wider distributionfor cross-correlations between CAZAC-based sequences with differentlengths.

The impact of large cross-correlations on the reception reliability ofsignals constructed from CAZAC-based sequences can be mitigated throughsequence hopping. Pseudo-random hopping patterns are well known in theart and are used for a variety of applications. Any such genericpseudo-random hopping pattern can serve as a reference for sequencehopping. In this manner, the CAZAC-based sequence used betweenconsecutive transmissions of ACK/NAK, CQI, or RS signals in differentSC-FDMA symbols, can change in a pseudo-random pattern and this reducesthe probability that CAZAC-based generated signals will be subjected tolarge mutual cross-correlations and correspondingly experience largeinterference over their transmission symbols.

There is therefore a need for supporting hopping of CAZAC-basedsequences with minimum implementation complexity in order to reduce theaverage interference among CAZAC-based sequences.

There is another need for assigning CAZAC-based sequences throughplanning in different Node Bs and different cells of the same Node B ina communication system.

Finally, there is a need for minimizing the signaling overhead forcommunicating sequence hopping parameters or the sequence assignment(planning) from the serving Node B to the UEs.

SUMMARY OF THE INVENTION

The present invention has been made to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention provides an apparatus and method for supporting CAZAC-basedsequence hopping or sequence planning.

Another aspect of the present invention enables CAZAC-based sequencehopping with minimum implementation complexity at a UE transmitter and aNode B receiver by applying the same hopping pattern to the sequencesused for signal transmission in all possible channels.

Additionally, an aspect of the present invention enables CAZAC-basedsequence hopping with minimum implementation complexity at a UEtransmitter and a Node B receiver by limiting the total number ofsequences in the sets of sequences for the possible resource blockallocations to be equal to the smallest number of sequences obtained forone of the possible resource block allocations.

A further aspect of the present invention enables CAZAC-based sequencehopping and planning with minimum signaling overhead for communicatingthe sequence allocation parameters from the serving Node B to UEs.

According to an aspect of the present invention, a method is providedfor transmitting a signal including a reference signal by a userequipment in a communication system. The method includes receiving, froma base station, information indicating whether sequence hopping isapplied or not; transmitting, to the base station, the signal using afirst sequence if a number of resource blocks allocated to the userequipment is less than a predetermined value; and transmitting, to thebase station, the signal using a second sequence to which the sequencehopping is applied based on the received information if the number ofthe resource blocks allocated to the user equipment is greater than orequal to the predetermined value. The sequence hopping is performedusing a pseudo-random function, and the sequence hopping is performed ina unit of a slot.

According to another aspect of the present invention, an apparatus isprovided for transmitting a signal including a reference signal in acommunication system. The apparatus includes a transceiver configured totransmit or receive data; and a controller coupled with the transceiverand configured to receive, from a base station, information indicatingwhether sequence hopping is applied or not, transmit, to the basestation, the signal using a first sequence if a number of resourceblocks allocated to the user equipment is less than 6, and transmit, tothe base station, the signal using a second sequence to which thesequence hopping allocated to the user equipment is applied based on thereceived information if the number of the resource blocks is greaterthan or equal to 6. The sequence hopping is performed using apseudo-random function, and the sequence hopping is performed in a unitof a slot.

According to another aspect of the present invention, a method isprovided for receiving a signal including a reference signal by a basestation in a communication system. The method includes transmittinginformation indicating whether sequence hopping is applied or not; andreceiving, from a user equipment, the signal based on the informationand a sequence. The sequence is determined as a first sequence if anumber of resource blocks allocated to the user equipment is less than apredetermined value. The sequence is determined as a second sequence towhich sequence hopping is applied based on the transmitted informationif the number of the resource blocks allocated to the user equipment isgreater than or equal to the predetermined value. The sequence hoppingis performed using a pseudo-random function, and the sequence hopping isperformed in a unit of a slot.

According to another aspect of the present invention, an apparatus isprovided for transmitting a signal including a reference signal in acommunication system. The apparatus includes a transceiver configured totransmit or receive data; and a controller coupled with the transceiverand configured to transmit information indicating whether sequencehopping is applied or not, and receive, from a user equipment, thesignal based on the information and a sequence. The sequence isdetermined as a first sequence if a number of resource blocks allocatedto the user equipment is less than a predetermined value. The sequenceis determined as a second sequence to which sequence hopping is appliedbased on the transmitted information if the number of the resourceblocks allocated to the user equipment is greater than or equal to thepredetermined value. The sequence hopping is performed using apseudo-random function, and the sequence hopping is performed in a unitof a slot.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a sub-frame structure for the SC-FDMAcommunication system;

FIG. 2 is a diagram illustrating a partitioning of a slot structure forthe transmission of ACK/NAK bits;

FIG. 3 is a diagram illustrating a partitioning of a slot structure forthe transmission of CQI bits;

FIG. 4 is a block diagram illustrating an SC-FDMA transmitter fortransmitting an ACK/NAK signal, or a CQI signal, or a reference signalusing a CAZAC-based sequence in the time domain;

FIG. 5 is a block diagram illustrating an SC-FDMA receiver for receivingan ACK/NAK signal, or a CQI signal, or a reference signal using aCAZAC-based sequence in the time domain;

FIG. 6 is a block diagram illustrating an SC-FDMA transmitter fortransmitting an ACK/NAK signal, or a CQI signal, or a reference signalusing a CAZAC-based sequence in the frequency domain;

FIG. 7 is a block diagram illustrating an SC-FDMA receiver for receivingan ACK/NAK signal, or a CQI signal, or a reference signal using aCAZAC-based sequence in the frequency domain;

FIG. 8 is a block diagram illustrating a construction of orthogonalCAZAC-based sequences through the application of different cyclic shiftson a root CAZAC-based sequence;

FIG. 9 is a diagram illustrating the CDF of cross-correlation values forCAZAC-based sequences of length 12;

FIG. 10 is a diagram illustrating the allocation of sequence groups todifferent cells or different Node Bs through group sequence planning,according to an embodiment of the present invention;

FIG. 11 is a diagram illustrating sequence hopping within a sub-framefor allocation larger than 6 RBs when group sequence planning is used,according to an embodiment of the present invention;

FIG. 12 is a diagram illustrating the allocation of sequence groups todifferent cells or different Node Bs through group sequence hopping,according to an embodiment of the present invention;

FIG. 13 is a diagram illustrating sequence hopping within a sub-framewhen group sequence hopping is used, according to an embodiment of thepresent invention;

FIG. 14 is a diagram illustrating allocating different sequences withdifferent cyclic shifts to cells of the same Node B, according to anembodiment of the present invention;

FIG. 15 is a diagram illustrating determining the PUCCH sequence fromthe PUSCH sequence, according to an embodiment of the present invention;and

FIG. 16 is a diagram illustrating determining the PUCCH sequence fromthe PUSCH sequence by applying a shift, according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention are described in detail withreference to the accompanying drawings. The same or similar componentsare designated by the same or similar reference numerals although theyare illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present invention.

Additionally, although the present invention assumes a SC-FDMAcommunication system, it also applies to all Frequency DivisionMultiplexing (FDM) systems in general and to Orthogonal FrequencyDivision Multiple Access (OFDMA), Orthogonal Frequency DivisionMultiplexing (OFDM), Frequency Division Multiple Access (FDMA), DiscreteFourier Transform (DFT)-spread OFDM, DFT-spread OFDMA, Single-CarrierOFDMA (SC-OFDMA), and Single-Carrier OFDM in particular.

Methods of the embodiments of the invention solve problems related tothe need for enabling sequence planning or sequence hopping forCAZAC-based sequences while minimizing the respective implementationcomplexity at a UE transmitter and at a Node B receiver and minimizingthe signaling overhead required for configuring the sequence planning orthe sequence hopping patterns.

As discussed in the foregoing background, the construction ofCAZAC-based sequences may be through various methods. The number ofsequences provided with cyclic extension or truncation of Zadoff-Chu(ZC) sequences depends on the sequence length. Some indicative valuesfor corresponding RB allocations are shown in Table 1 where one RB isassumed to consist of 12 sub-carriers.

TABLE 1 Number of CAZAC-based Sequences from Cyclic Extension of ZCSequences Number of Sequences Number of RBs Number of Sub-Carriers fromZC Extension 1 12 10 (prime is 11) 2 24 22 (prime is 23) 3 36 30 (primeis 31) 4 48 46 (prime is 47) 5 60 58 (prime is 59) 6 72 70 (prime is 71)8 96 88 (prime is 89) 9 108 106 (prime is 107) 10 120 112 (prime is 113)

Since the number of CAZAC-based sequences depend on the correspondingsequence length, a number of sequences of larger length can beassociated with each sequence of smaller length. For example, referringto Table 1, for cyclic extension of ZC sequences, each of the 10sequences of length 12 can be associated (one-to-one mapping) with a setof 7 sequences of length 72 (since there are 70 sequences of length 72).Moreover, the number of sequences for small RB allocations, such as 1 RBor 2 RBs, is the smallest and defines the constraints in allocatingdifferent sequences in neighboring cells and Node Bs (a Node B maycomprise of multiple cells). For these sequences, if a pseudo-randomhopping pattern applies for their transmission, the same sequence mayoften be used in neighboring cells resulting to full interference oftransmissions and associated degradation in the reception reliability ofsignals transmitted through the use of CAZAC-based sequences.

To mitigate the sequence allocation problem resulting from the smallnumber of available CAZAC-based sequences for the smaller RBallocations, CAZAC sequences constructed through computer searches canbe used as a larger number of sequences can be obtained in this manner.However, unlike CAZAC-based sequences obtained from cyclic extension ortruncation of ZC sequences, a closed form expression for computergenerated CAZAC sequences does not exist and such sequences need to bestored in memory. For this reason, their use is typically confined tosmall RB allocations where the shortage of CAZAC-based sequences is mostacute. For the larger RB allocations, CAZAC-based sequences aregenerated through the implementation of a formula such as the onedescribed for the generation of ZC sequences. About 30 computergenerated CAZAC sequences can be obtained for 1 RB allocations and byobtaining the same number of sequences for 2 RB allocations, sequenceplanning and sequence hopping is then constrained by the number ofsequences for 1, 2, or 3 RB allocations. In an embodiment this number is30.

The invention considers cyclic extension of ZC sequences for thegeneration of CAZAC-based sequences for allocations equal to or largerthan 3 RBs and computer generated CAZAC sequences for allocations of 1RB or 2 RBs.

An embodiment of the invention assumes that PUCCH transmissions from aUE occupy one RB and allocations larger than 1 RB are used only for thePUSCH, which, in the embodiment, contains 2 RS transmission symbols persub-frame. Therefore, only one sequence hopping opportunity existswithin a PUSCH sub-frame.

For packet retransmissions based on Hybrid Automatic Repeat reQuest(HARQ), as it is known in the art, the interference experienced by theCAZAC-based sequence used for RS transmission will be different amongretransmissions as different RB allocations (different size or differentBW position leading to partial overlapping between two CAZAC sequences)are likely to be used for UEs in interfering cells during a packetretransmission. Moreover, the channel characteristics are likely to bedifferent between retransmissions and this also leads to differentcross-correlation characteristics among interfering CAZAC sequences.Therefore, extending the number of sequences for each RB allocation tomore than 2 is of little or no benefit to the PUSCH reception quality.

For the above reasons, the invention considers the use of only a sub-setof sequences from the total set of available ones. These sequences maybe fixed and selected according to their cross-correlation and/oraccording to their cubic metric values where small values are desired inboth cases. Limiting the number of sequences that can be used forhopping for the larger RB allocations, reduces the number of sequencegroups and corresponding hopping patterns that need to be supported andtherefore reduces the complexity and signaling overhead to supportsequence hopping.

Considering that the limitation of sequences, and therefore thelimitation in hopping patterns, occurs for the smaller RB allocationsand that an embodiment of the invention assumes 2 RS per PUSCHsub-frame, one sequence for small RB allocations can be associated withtwo sequences for the larger RB allocations. As the embodiment assumes30 computer generated CAZAC sequences for 1 RB and 2 RB allocations, thegrouping of sequences for different RB allocations results in 30 groupswhere each group includes one CAZAC-based sequence for allocations up to5 RBs and two CAZAC sequences for allocations larger than 5 RBs (Table1). The sequences in each group are different.

The grouping principle is summarized in Table 2. In an embodiment of thepresent invention, there are 30 sequence groups (one-to-one mapping isassumed between each sequence group and each sequence in a set of 30sequences). Considering the number of available sequences from Table 1,it becomes apparent that only a sub-set of sequences is used forallocations of 4 RBs (30 out of set of 46 sequences are used), 5 RBs (30out of set of 58 sequences are used), and 6 RBs or larger (60 out of aset of 70 or more sequences are used). As previously mentioned, thesub-set of these sequences may be fixed and selected for itscross-correlation and/or cubic metric properties. Therefore, the numberof sequence groups is equal to the smallest sequence set size, which inthe embodiment is equal to 30, with each group containing one sequencefor allocations up to 5 RBs and two sequences for allocations largerthan 5 RBs, and each set containing 30 sequences for allocations smallerthan or equal to 5 RBs and 60 sequences for allocations larger than 5RBs.

TABLE 2 Number of Sequences per Sequence Group. Number of RBs Number ofSequences per group 1 1 2 1 3 1 4 1 5 1 6 2 8 2 9 2 10 or larger 2

The invention considers that the CAZAC sequence allocation to cells orNode Bs is either through planning or hopping. If both sequence planningand sequence hopping could be supported in a communication system, theUEs are informed of the selection for planning or hopping through arespective indicator broadcasted by the Node B (one bit is needed toindicate whether sequence planning or sequence hopping is used).

Sequence planning assigns each of the 30 groups of sequences, with eachgroup containing 1 sequence for allocations up to 5 RBs and 2 sequencesfor allocations larger than 5 RBs, to neighboring cells and Node Bs sothat the geographical separation between cells using the same group ofsequences is preferably maximized. The assignment may be explicitthrough broadcasting of group sequence number, which in an embodimenthaving 30 sequence groups can be communicated through the broadcastingof 5 bits, or it can be implicit by associating the group sequencenumber to the cell identity. This is equivalent to specifying onesequence from the set of sequences with the smallest size (because aone-to-one mapping between each of these sequences and each group ofsequences is assumed). In the embodiment this can be either of the setsof 30 sequences corresponding to 1, 2, or 3 RB allocations.

This principle is illustrated in FIG. 10 for cell based and Node B basedsequence group allocation (a Node B is assumed to serve 3 cells). Forcell based sequence group assignment, different cells, such as, forexample cells 1010 and 1020, are assumed to be allocated differentsequence groups. For Node B based sequence group assignment, differentcells, such as, for example Node Bs 1030 and 1040, are assumed to beallocated different sequence groups. Obviously, after exhausting allsequence groups, having the same sequence group in cells or Node Bscannot be avoided but the objective is to have large geographicalseparation among such cells or Node Bs so that the interference causedfrom using the same sequences is negligible.

Sequence hopping may still apply between the pair of sequences forallocations of 6 RBs or larger during the two RS transmission symbols ofthe PUSCH sub-frame as illustrated in FIG. 11. This provides additionalrandomization of the cross-correlations among sequences transmitted fromUEs in different cells and thereby provides more robust receptionreliability than the one achieved purely through sequence planning. Nohopping applies for the sequences with length smaller than 6 RBsassuming that all sequence groups are used for planning. Therefore, ifthe PUSCH allocation to a UE is smaller than 6 RBs, the same CAZACsequence is used for the RS transmission symbols 1110 and 1120 while ifthe PUSCH allocation is 6 RBs or larger, a different CAZAC sequence,among 2 possible CAZAC sequences, is used for the RS transmission ineach of the symbols 1110 and 1120.

If sequence planning is not used, the invention assumes that sequencehopping applies instead for the sequences used for RS transmissionbetween successive transmission instances for any possible RBallocation. The RS transmission in the two symbols of the PUSCHsub-frame in FIG. 1 is based on sequences from two typically differentgroups of sequences. However, in order to limit the complexity andsignaling required to define the sequence hopping patterns and sincethere is no additional benefit from having more than one sequence pergroup for allocations larger than 5 RBs when sequence hopping is used,only one sequence for each RB allocation exists for any of the 30 groupsof sequences. In other words, only one sequence is selected to be usedfor each of the possible RB allocations (all entries in Table 2 contain1 sequence) and all sets of sequences contain the same number ofsequences, which is the same as the number of sequence groups. FIG. 12and FIG. 13 further illustrate this concept. In FIG. 12, differentsequence groups such as 1210 and 1230 or 1220 and 1240 are used duringdifferent transmission periods in each cell.

In FIG. 13, the sequence used by a UE during successive RS transmissions1310 and 1320 varies according to a sequence hopping pattern which isinitialized either explicitly through broadcast signaling in each cellor implicitly through the broadcasted cell identity. The sequencehopping pattern may be the same for all cells and only itsinitialization may be cell dependent by specifying the initial sequencegroup or, equivalently, by specifying the initial sequence for an RBallocation since one-to-one mapping between each sequence in a set andeach sequence group is assumed. The first transmission period maycorrespond to the first slot of the first sub-frame in a period of oneframe (for example, a frame may comprise of 10 sub-frames) or to anyother predetermined transmission instance. The same concept can betrivially extended to Node B specific sequence hopping.

Sequence hopping for both PUCCH signals (ACK/NAK, CQI, and RS) and thePUSCH RS can also be supported and the respective signaling issubsequently considered.

In order to maximize the PUCCH UE multiplexing capacity, all cyclicshifts (CS) of a CAZAC sequence are assumed to be used for the PUCCHtransmission within a cell thereby necessitating the use of differentCAZAC sequences in different cells (FIG. 10 with cell based groupallocation). However, for the PUSCH, this depends on the extent of theapplication of Spatial Domain Multiple Access (SDMA) as it is known inthe art. With SDMA, multiple UEs share the same RBs for their PUSCHtransmission (no SDMA applies for the PUCCH as all CS are assumed to beused in each cell).

Without SDMA or with SDMA applied to a maximum of 4 UEs per cell,assuming that 12 CS can be used, the same CAZAC sequence may be usedamong the adjacent cells of the same Node B with different CS used todiscriminate the PUSCH RS in each cell as shown in FIG. 14 which iscombined with FIG. 10 for the case of Node B based sequence groupallocation. Cells 1410, 1420, and 1430 use the same sequence group, thatis the same CAZAC based sequence for any given PUSCH RB allocation, butuse different CS in order to separate the sequences.

With SDMA applied to more than 4 UEs per cell (with 3 cells per Node B),it may not be possible to rely on the use of different CS to separatethe PUSCH RS from UEs in different cells. Then, a different CAZAC-basedsequence needs to be used per cell as is the case for the PUCCH (FIG. 10with cell based group allocation). Regardless of the separation methodfor the PUSCH RS from UEs in different cells of a Node B (throughdifferent CS of the same CAZAC-based sequence or through differentCAZAC-based sequences), the present invention considers that thesequence hopping pattern for the PUCCH is derived from the signaledsequence hopping pattern for the PUSCH (the reverse may also apply).

If different CAZAC-based sequences are used for the PUSCH RStransmission in the cells of a Node B (FIG. 10 with cell based groupallocation), for example through sequence planning, the inventionconsiders that the same CAZAC sequence can be used for 1 RB allocationsof the PUSCH RS and for the PUCCH (for which the signal transmissionsare assumed to be always over 1 RB). Therefore, the initial sequencegroup assignment for the PUSCH, either through explicit signaling in abroadcast channel in the serving cell or through implicit mapping to thebroadcasted cell identity, determines the sequence used for the PUCCHtransmission. This concept is illustrated in FIG. 15.

It should be noted that PUCCH signals (RS and/or ACK/NAK and/or CQI) mayallow for more sequence hopping instances within a sub-frame(symbol-based sequence hopping), but the same hopping pattern can stillapply as it only needs to have a longer time scale for the PUSCH RS. Ifthe sequence hopping for PUCCH signals is slot based and not symbolbased, the PUSCH and PUCCH use the same sequence hopping patterns.

If the same CAZAC sequence is used for the PUSCH RS transmission indifferent cells of the same Node B (FIG. 10 with Node B based sequencegroup allocation), the sequence hopping pattern for the PUCCHtransmission may still be determined by the sequence hopping pattern ofthe PUSCH RS transmission even though different CAZAC sequences are usedin each cell of the same Node B for the PUCCH transmission. This isachieved by the Node B signaling only a shift of the initial sequenceapplied to the PUSCH RS transmission, with this shift corresponding toinitializing the sequence hopping pattern with a different CAZACsequence in the set of CAZAC sequences over 1 RB for the PUCCH. Clearly,as it is subsequently illustrated in FIG. 16, the addition of a shiftvalue S is cyclical over the set of sequences, meaning that the shiftvalue S is applied modulo the size of the sequence set K, wherein themodulo operation is as known in the art. Therefore, in mathematicalterms, if the hopping pattern for the PUSCH is initialized with sequencenumber N, the hopping pattern for the PUCCH is initialized, in therespective sequence set, with sequence number M=(N+S) mod(K) where(N+S)mod(K)=(N+S)−floor((N+S)/K)·K and the “floor” operation rounds anumber to its lower integer as it is known in the art.

The shift can be specified by a number of bits equal to the number ofsequences for the RB allocation of PUCCH signals. If the PUCCH RBallocation is the smallest one corresponding to 1 RB, this number isidentical to the number of sequence groups (in the embodiment, 5 bitsare needed to specify one of the 30 sequences in a set of sequences or,equivalently, one of the 30 sequence groups). Alternatively, suchsignaling overhead can be reduced by limiting the range of the shift toonly the sequences with indexes adjacent to the ones used for the by thefirst sequence in the hopping pattern applied to the RS transmission forthe data channel. In that case, only 2 bits are needed to indicate theprevious, same, or next sequence.

The above are illustrated in FIG. 16 where in an embodiment, a shift of0 1610, 1 1620, and −1 1630 is applied to the sequence hopping patternof the PUCCH transmission in three different cells relative to thesequence hopping pattern for the PUSCH RS transmission 1640. Thedifferent sequence hopping patterns simply correspond to a cyclicalshift (the addition of the shift value is modulo the sequence set size)of the same sequence hopping pattern 1640, or equivalently, thedifferent sequence hopping patterns correspond to differentinitialization of the same hopping pattern. The initialization of thehopping pattern for the PUSCH may be explicitly or implicitly signaled,as previously described, and the shift for the initialization patternfor the PUCCH is determined relative to the initial sequence for thePUSCH (which may be different than the first sequence in the set ofsequences). The above roles of the PUSCH and PUCCH may be reversed andthe shift may instead define the initialization of the PUSCH, instead ofthe PUCCH, hopping pattern in a cell. The start of the hopping patternin time may be defined relative to the first slot in the first sub-framein a frame or a super-frame (both comprising of multiple sub-frames) asthese notions are typically referred to in the art.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims.

What is claimed is:
 1. A method performed by a user equipment in acommunication system, the method comprising: in case that a grouphopping is enabled, selecting a first sequence in a first sequence groupamong 30 sequence groups; and transmitting a first reference signalbased on the selected first sequences; and in case that the grouphopping is disabled and a sequence length associated with a secondreference signal is greater than or equal to 6 resource blocks (RBs),selecting a second sequence by a sequence hopping in a second sequencegroup consisting of two sequences, and transmitting the second referencesignal based on the selected second sequence, wherein the sequencehopping is performed in a unit of a slot.
 2. The method of claim 1,wherein the first sequence and the second sequence include a constantamplitude zero auto-correlation (CAZAC)-based sequence.
 3. The method ofclaim 1, wherein the sequence length associated with the secondreference signal corresponds to a number of RBs allocated to the userequipment.
 4. The method of claim 1, further comprising receiving, froma base station, information indicating that the group hopping is enabledor disabled.
 5. The method of claim 1, wherein the sequence hopping isperformed using a random function.
 6. A user equipment in acommunication system, the user equipment comprising: a transceiver; anda controller configured to: in case that a group hopping is enabled,select a first sequence in a first sequence group among 30 sequencegroups, and transmit, via the transceiver, a first reference signalbased on the selected first sequence, and in case that the group hoppingis disabled and a sequence length associated with a second referencesignal is greater than or equal to 6 resource blocks (RBs), select asecond sequence by a sequence hopping in a second sequence groupconsisting of two sequences, and transmit, via the transceiver, thesecond reference signal based on the selected second sequence, whereinthe sequence hopping is performed in a unit of a slot.
 7. The userequipment of claim 6, wherein the first sequence and the second sequenceinclude a constant amplitude zero auto-correlation (CAZAC)-basedsequence.
 8. The user equipment of claim 6, wherein the sequence lengthassociated with the second reference signal corresponds to a number ofRBs allocated to the user equipment.
 9. The user equipment of claim 6,the controller is further configured to receive, via the transceiverfrom a base station, information indicating that the group hopping isenabled or disabled.
 10. The user equipment of claim 6, wherein thesequence hopping is performed using a random function.
 11. A methodperformed by a base station in a communication system, the methodcomprising: receiving, from a user equipment, a first reference signalbased on a first sequence in a first sequence group among 30 sequencegroups, in a case that a group hopping is enabled; and receiving, fromthe user equipment, a second reference signal based on a second sequenceto which the sequence hopping is applied in a second sequence groupconsisting of two sequences, in case that the group hopping is disabledand a sequence length associated with the second reference signal isgreater than or equal to 6 resource blocks (RBs), wherein the sequencehopping is applied in a unit of a slot.
 12. The method of claim 11,wherein the first sequence and the second sequence include a constantamplitude zero auto-correlation (CAZAC)-based sequence.
 13. The methodof claim 11, wherein the sequence length associated with the secondreference signal corresponds to a number of RBs allocated to the userequipment.
 14. The method of claim 11, further comprising transmitting,to the user equipment, information indicating that the group hopping isenabled or disabled.
 15. The method of claim 11, wherein the sequencehopping is applied using a random function.
 16. A base station in acommunication system, the base station comprising: a transceiver; and acontroller configured to: receive, via the transceiver, from a userequipment, a first reference signal based on a first sequence in a firstsequence group among 30 sequence groups, in case that a group hopping isenabled, and receive, via the transceiver, from the user equipment, asecond reference signal based on a second sequence to which the sequencehopping is applied in a second sequence group consisting of twosequences, in case that the group hopping is disable and a sequencelength associated with the second reference signal is greater than orequal to 6 resource blocks (RBs), wherein the sequence hopping isapplied in a unit of a slot.
 17. The base station of claim 16, whereinthe first sequence and the second sequence include constant amplitudezero auto-correlation (CAZAC)-based sequence.
 18. The base station ofclaim 16, wherein the sequence length associated with the secondreference signal corresponds to a number of RBs allocated to the userequipment.
 19. The base station of claim 16, wherein the controller isfurther configured to transmit, to the user equipment, via thetransceiver, information indicating that the group hopping is enabled ordisabled.
 20. The base station of claim 16, wherein the sequence hoppingis applied using a random function.